Millions of Americans were battling a heat wave Wednesday, facing blazing temperatures and thick humidity which will make the summer scorcher only feel worse.
Excessive heat warnings were in effect from St. Louis down the Mississippi River and past Memphis — into northeastern Louisiana and including Philadelphia. In total, around 35 million people will be under some sort of heat advisory on Wednesday, according to The Weather Channel.
The sweltering heat is expected to last unusually long, Weather Channel meteorologist Kevin Roth said.
"Most of the country over the next week will see temperatures of 90 or higher," Roth said. "There's not going to be very much relief."
After a blazingly hot Tuesday — with temperatures hitting 94 degrees in New York City — the northwest and northeast were bracing for more tropical weather.
Roth said that the northwest will see temperatures 10-20 degrees above average, with record-setting heat likely on Thursday and through the weekend. The northeast will see highs 5-10 degrees above average.
Several towns and cities in Connecticut were opening cooling centers in anticipation, according to NBC Connecticut.
Oppressive humidity will make it even worse for the Mississippi Valley, according to Roth.
St. Louis might only see temperatures of around 91 — but it'll feel like 102 or higher.
The most dangerous heat is forecast for Missouri and Memphis, with predictions that the heat index could climb to 110. Texas and Florida, too, will see temperatures top 100 degrees.
Even the typically cool great lakes are expected to see the mercury rise above 90 degrees for the first time since 2013.
Staying cool isn't the only thing to worry about, however: environmental officials have warned the hot and humid weather will produce poor air quality in southern Connecticut, coastal Rhode Island and southeastern Massachusetts.
This article originally appeared on NBCNews.com.